Real 3D-Printed Engine That Runs

A hobbyist named Alexander has done something most engineers would call impractical: he built a working internal combustion engine, mostly from spools of plastic filament.

Using a desktop 3D printer and materials like ASA, ABS, and carbon-fiber-reinforced PET, Alexander spent years and at least three attempts crafting the AP3 Carbon D125, a 125cc single-cylinder four-stroke engine of the kind you'd find in a scooter.

Earlier versions were humbling. One ran for just four minutes before heat melted the cylinder body entirely. Oil mixed with water. Torque couldn't be applied evenly. He essentially started over.

This time, he printed an oil pump directly into the crankcase, redesigned the cooling system with a mechanical water pump, and used a copper-wire head gasket rated for 1,000 degrees Celsius.

The engine started, idled steadily, and held compression. Every printed part survived the heat and vibration. Alexander says seeing oil flow through the gallery during a bench test gave him the confidence to believe it could actually work.

It did.